A bias modulation method utilizing a magneto-static interaction between a wedge-formed pattern made of a non-magnetostrictive soft magnetic material such as Permalloy and magnetic bubbles (cylindrical domains or localized highly stable magnetic states) and operable for conveying magnetic bubbles toward a desired direction is disclosed the article Application of Orthoferrites to Domain Wall Devices by A. H. Bobeck et al in IEEE Trans. on Mag, MAG-5 (1969) PP. 544-553.
In this method, a series of wedge-formed patterns made of a non-magnetostrictive high premeability thin film are continuously disposed on a thin plate made of a magnetic bubble forming material such as an orthoferrite and the expansion and contraction of the magnetic bubbles due to the variation of a biasing magnetic field are converted into an effective unidirectional movement of the magnetic bubbles.
This method involves a disadvantage in that the wedge-formed patterns are made of a optically opaque material (permalloy) which disturbs the observation of the magnetic bubbles when the latter are used as image forming elements.